Buffalo, N.Y. -- An electrical engineer at the University at
Buffalo, who previously demonstrated experimentally the "rainbow
trapping effect" -- a phenomenon that could boost optical data
storage and communications -- is now working to capture all the
colors of the rainbow.

In a paper published March 29 in the Proceedings of the National
Academy of Sciences, Qiaoqiang Gan (pronounced "Chow-Chung" and
"Gone"), PhD, an assistant professor of electrical engineering at
the University at Buffalo's School of Engineering and Applied
Sciences, and his colleagues at Lehigh University, where he was a
graduate student in Dr. Filbert Bartoli's group, described how they
slowed broadband light waves using a type of material called
nanoplasmonic structures.

Gan explains that the ultimate goal is to achieve a breakthrough
in optical communications called multiplexed, multiwavelength
communications, where optical data can potentially be tamed at
different wavelengths, thus greatly increasing processing and
transmission capacity.

He notes that it is widely recognized that if light could ever
be stopped entirely, new possibilities would open up for data
storage.

"At the moment, processing data with optical signals is limited
by how quickly the signal can be interpreted," he says. "If the
signal can be slowed, more information could be processed without
overloading the system."

Gan and his colleagues created nanoplasmonic structures by
making nanoscale grooves in metallic surfaces at different depths,
which alters the materials' optical properties.

These plasmonic chips provide the critical connection between
nanoelectronics and photonics, Gan explains, allowing these
different types of devices to be integrated, a prerequisite for
realizing the potential of optical computing, "lab-on-a-chip"
biosensors and more efficient, thin-film photovoltaic
materials.

According to Gan, the optical properties of the nanoplasmonic
structures allow different wavelengths of light to be trapped at
different positions in the structure, potentially allowing for
optical data storage and enhanced nonlinear optics.

The structures Gan developed slow light down so much that they
are able to trap multiple wavelengths of light on a single chip,
whereas conventional methods can only trap a single wavelength in a
narrow band.

"Light is usually very fast, but the structures I created can
slow broadband light significantly," says Gan. "It's as though I
can hold the light in my hand."

That, Gan explains, is because of the structures' engineered
surface "plasmon resonances," where light excites the waves of
electrons that oscillate back and forth on metal surfaces.

In this case, he says, light can be slowed down and trapped in
the vicinity of resonances in this novel, dispersive structural
material.

Gan and his colleagues also found that because the nanoplasmonic
structures they developed can trap very slow resonances of light,
they can do so at room temperature, instead of at the ultracold
temperatures that are required in conventional slow-light
technologies.

"In the PNAS paper, we showed that we trapped red to green,"
explains Gan. "Now we are working on trapping a broader wavelength,
from red to blue. We want to trap the entire rainbow."

Gan, who was hired at UB under the UB 2020 strategic strength in
Integrated Nanostructured Systems, will be working toward that
goal, using the ultrafast light source in UB's Department of
Electrical Engineering in the laboratory of UB professor and vice
president for research Alexander N. Cartwright.

"This ultrafast light source will allow us to measure
experimentally just how slow is the light that we have trapped in
our nanoplasmonic structures," Gan explains. "Once we know that, we
will be able to demonstrate our capability to manipulate light
through experiments and optimize the structure to slow the light
further."

Co-authors with Gan on the study are Filbert Bertoli, Yongkang
Gao, Yujie Ding, Kyle Wagner and Dmitri Vezenov, all of Lehigh
University.

The University at Buffalo is a premier research-intensive
public university, a flagship institution in the State University
of New York system and its largest and most comprehensive campus.
UB's more than 28,000 students pursue their academic interests
through more than 300 undergraduate, graduate and professional
degree programs. Founded in 1846, the University at Buffalo is a
member of the Association of American Universities.

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